3 I O CLASS I PICA TION OF VER TEBRA TES. 



tropics the terrestrial species sleep through the dry season 

 The group appears in the Permian of North America, and has 

 continued until the present. 



SUB-ORDER i. CHELYDOSAURIA. 



No temporal fossa ; carapace of transverse osseous arches in close con- 

 tact, extending across the back from side to side. Vertebrae amphicoelous ; 

 limbs ambulatory. This sub-order, represented by Otoccelus from the Per- 

 mian of North America, is regarded by Cope as ancestral to the other 

 chelonia and the pseudosuchian crocodilia. 



SUB-ORDER 2. ATHEC^E. 



Turtles without scales but with a leathery skin, carapace of polygonal 

 dermal bony plates arranged in rows, unconnected with ribs and vertebrae ; 

 plastron poorly developed, with large central fontanelle ; episternum lacking. 

 Skull without descending process of parietals. Feet flipper-like, claws lack- 

 ing. Dermochelys (Sp/iargis) coriacea, the leather-back tortoise, occurs 

 in all warmer seas, extending north to Cape Cod. It weighs occasionally 

 i,5oolbs. The sub-order appears (Psephoderma) in the trias. Protostega, 

 cretaceous of Kansas. 



SUB-ORDER 3. TRIONYCHIA. 



Turtles with the carapace poorly ossified, ribs and vertebrae being 

 connected with it. Scales lacking, the body covered with a leathery skin ; 

 marginal bones few or absent. Plastron with episternum and a large me- 

 dian fontanelle ; sacral and caudal ribs articulating with neural arches. 

 A descending process of the parietals present. Feet webbed, three claws 

 on each foot. The sub-order appears in the upper cretaceous of New 

 Jersey, and is represented by over thirty species to-day, all inhabitants of 

 fresh water, and best developed in the Oriental regions. All are carnivor- 

 ous. Four species of leather turtle (A my da) and soft-shell turtles (As- 

 pidonectes} in the U. S. 



SUB-ORDER 4. CRYPTODIRA. 



Turtles with well-ossified carapace, connected with internal skeleton ; 

 epidermal scales and marginal ossicles present ; an episternum ; pelvis free 

 from plastron ; caudal ribs articulated to vertebral centra. A descending 

 process to the parietals. The species are numerous, the more important 

 families being the following: CHELONID^E, with heart-shaped carapace, and 

 paddle-like feet, bearing at most two claws. The costal plates do not 

 reach the marginals. Thalassochelys caretta, the loggerhead turtle, weighs 

 450 Ibs. Eretmochelys imbricata, the tortoise-shell turtle, is smaller. The 

 green turtle, Chelone my das, may weigh 850 Ibs. It is highly esteemed as 



